The present invention relates to a seal for sealing between a stator shroud and a leading edge of a nozzle wall along the outer band of a nozzle segment defining in part the hot gas path through the gas turbine.
In an industrial gas turbine, shroud segments are fixed to turbine shell hooks in an annular array to form an annular shroud radially outwardly and adjacent the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Typically, nozzles are hooked into the radial slots in the shroud segments. However, the cavities forward and aft of the shroud segments are at a higher pressure than the pressure of the gas path and significant leakage into the hot gas path frequently occurs. These cavities are typically pressurized by compressor discharge air and leakage of this air is detrimental to turbine performance and emissions. The leakage is compounded in those nozzle stages having non-continuous nozzle leading edge hooks. That is, the gaps between the hooks and adjacent the edges of the shrouds provide large leakage paths for compressor discharge air to flow into the hot gas flow path. It is therefore desirable to provide a seal effective between the stator shroud segments and the nozzle wall, particularly in those turbines having non-continuous nozzle hooks, to minimize leakage flow into the hot gas path.
In accordance with a preferred embodiment of the present invention, there is provided a shroud system affording an effective seal between the shroud segments and the nozzle side wall band, particularly the leading edge side wall of the nozzle band. Particularly, inner and outer shrouds are provided with complementary hooks and grooves adjacent the leading and trailing edges of each shroud for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to a turbine shell hook. In a preferred embodiment, each shroud segment has one outer shroud and two inner shrouds. The shroud segments form an annular array thereof about the turbine rotor axis to form a shroud set. More particularly, the leading edge of the adjacent nozzle side wall band has a forward projection or xe2x80x9cnubxe2x80x9d for interfacing with a shroud leaf seal adjacent the trailing edge of the shroud segment. The leaf seal may be mounted on either the two inner shrouds or on the outer shroud. The leaf seal spans the circumference of the shroud segment and is spring-loaded in an aft direction by a pair of spring clips. The leaf seal and spring clips are pinned to the shroud segment in a radially outwardly extending groove along the shroud segment. To create the smallest leakage possible employing a leaf seal engaging against the nub or flange of the leading edge side wall of the outer band of the nozzle, the leaf seal is pivoted to the shroud segment such that it extends perpendicular to the turbine centerline during operation. The seals are also provided with overlaps such that each overlap seals between adjacent leaf seals of adjacent segments.
In a preferred embodiment according to the present invention, there is provided a seal for sealing between a stator shroud and a nozzle of a gas turbine to substantially preclude leakage between a pressurized cavity on one side of the seal and hot gases in a hot gas path of the gas turbine on the other side of the seal, comprising a shroud segment having a surface for, in part, defining the hot gas path and overlying tips of buckets forming part of a turbine rotor, an outer band for, in part, defining the hot gas path and forming part of the nozzle of the turbine, a leaf seal between the shroud segment and the nozzle outer band and a spring engaging the shroud segment and the leaf seal for biasing the leaf seal into sealing engagement with the nozzle outer band.
In a further preferred embodiment according to the present invention, there is provided a seal for sealing between a stator shroud and a nozzle of a gas turbine to substantially preclude leakage between a pressurized cavity on one side of the seal and hot gases in a hot gas path of the gas turbine on the other side of the seal, comprising a shroud segment having a surface for, in part, defining the hot gas path and overlying tips of buckets forming part of a turbine rotor, the shroud segment having a leading edge and a trailing edge, an outer band for, in part, defining the hot gas path and forming part of the nozzle of the turbine, a leaf seal between the trailing edge of the shroud segment and a leading edge side wall of the nozzle outer band, the shroud segment having a seat for receiving the leaf seal and a spring engaging the shroud segment and the leaf seal for biasing a portion of the leaf seal into sealing engagement with the leading edge side wall of the nozzle outer band.